Liver cancer is the fifth most common cancer and the third leading cause of cancer mortality in the world. Hepatocelluar carcinoma (HCC) accounts for approximately 75% of liver cancer cases, while intrahepatic cholangiocarcinoma (ICC) is the second most common primary liver tumor. There is an urgent need to develop new drugs for the treatment of liver cancer. Project 1: Targeting GPC3 in HCC and other cancers GPC3 is a heparan sulfate proteoglycan highly expressed in HCC and holds potential for liver cancer therapy. The biological functions of GPC3 and its role in liver tumorigenesis remain elusive. Our work helps uncover the role of GPC3 in liver cancer cell growth. We produced and analyzed a recombinant soluble GPC3 (25-559) that inhibited the growth of HCC cells and presumed to compete with endogenous glypican-3 for binding to growth factors on the cancer cell surface. Our lab isolated a panel of mouse monoclonal antibodies including YP7 that recognize the C-terminal end (511-560) of GPC3. YP7 binds GPC3 with high affinity for HCC. It is highly sensitive in that it also detects GPC3 in low expression ovarian clear cell carcinoma and melanoma cells. In FY13, the GPC3 mouse monoclonal antibody work was reported in the journal MAbs (PMID: 22820551). Recently, we generated a human single-domain antibody, HN3, with high affinity for cell-surface-associated GPC3 molecules. The human antibody recognizes a unique conformational epitope in the core protein of GPC3. HN3 inhibits proliferation of HCC cells and exhibits significant inhibition of HCC xenograft tumor growth in mice. The underlying mechanism of HN3 action may involve cell-cycle arrest at G1 phase through Yes-associated protein (YAP) signaling, suggesting a novel mechanism for GPC3-targeted cancer therapy. In FY13, the HN3 antibody research was published in Proc Natl Acad Sci USA (PMID: 23471984). Project 2: Targeting mesothelin in ICC and other cancers Mesothelin is expressed at high levels in ICC, mesothelioma, ovarian cancer, and other cancers. The interaction between mesothelin and MUC16 (also known as CA125) may facilitate the implantation and spread of tumors. We experimentally established the 64-amino acid functional binding domain (IAB, 296-359) in the N-terminus of cell surface mesothelin for MUC16. HN125, an immunoadhesin that consists of the IAB domain and the Fc portion of a human antibody, disrupts the cancer cell adhesion mediated by the MUC16-mesothelin interaction, and elicits antibody-dependent cell mediated cytotoxicity against MUC16-positive tumor cells. Subsequently, we generated the HN1 and SD1 human monoclonal antibodies. HN1 binds the N-terminal end of cell surface mesothelin, disrupts the mesothelin-MUC16 interaction and elicits antibody-dependent cell mediated cytotoxicity against tumor cells. SD1 is a human single-domain antibody that recognizes the C-terminal end (539-588) of mesothelin close to the cell surface and exhibits complement-dependent cytotoxicity against tumor cells. In FY13, the SD1 human antibody to mesothelin was reported in Mol Cancer Ther (PMID: 23371858). The new human antibodies show potential for use as cancer therapeutic candidates.